Our studies have further defined the role of oxygen radicals in models of immune inflammation in vitro and their potential bactericidal role in the gingival crevice, in vivo. Studies of the role of oxygen radicals in the suppression of lymphocyte responses by undegradable particles were concluded during this reporting period. These studies implicated oxidative damage as the mechanism of inhibition in an in vitro model of a low turnover granuloma. Preliminary studies of the thiol metabolism of murine spleen cells were initiated. These studies were predicated on the hypothesis that spleen cells protect themselves against oxidative damage by actively cleaving extracellular disulfide to free thiols. An assay for the measure of extracellular thiols in cultures was developed during this period. Finally studies of the crevicular neutrophils of normal, healthy adults were concluded. These studies showed that these cells have viability, oxidative metabolism, phagocytic capacity and chematactic responsiveness equal to those of peripheral blood neutrophils. Thus crevicular neutrophils are fully functional as protective cells in the sulcus.